IRE1/XBP1s signaling: a novel essential regulator for bone marrow microenvironmen

描述（由申请人提供）： 多发性骨髓瘤（MM）是最常见的累及骨骼的癌症，并诱导在中轴骨和颅面骨中很少愈合的溶骨性病变。多发性骨髓瘤骨疾病（MMBD）是负责MM的一些最具破坏性的并发症，是与MM相关的发病率的主要来源。骨髓基质细胞（BMSC）是驻留在MM微环境中的主要类型的细胞。研究表明，在MMBD中，BMSC产生多种生长因子和炎性细胞因子。这些因子可以促进骨髓瘤肿瘤细胞的生长，并激活破骨细胞（骨吸收细胞），以诱导骨中的溶骨性病变。因此，破坏BMSC对MM细胞生长和破骨细胞形成的支持在治疗MMBD中具有重要的临床意义。我们的长期目标是阐明MMBD中调节BMSC支持MM细胞生长和骨破坏的分子机制，并确定破坏BMSC支持MMBD的潜在治疗靶点。为了实现这一目标，我们已经发现，细胞应激分子剪接的X-box-binding蛋白1（XBP 1 s）诱导骨髓基质细胞来源于MM患者，与那些来自健康供体。在其他器官和疾病模型（如炎症性肠病）中，XBP 1 s已被证明可以控制炎症细胞因子的基因表达和/或蛋白质分泌。我们最近发现，在健康供体BMSC中，XBP 1 s蛋白水平的升高诱导了通常存在于MM患者BMSC中的病理行为，例如，升高的炎性细胞因子分泌，增强对MM细胞生长和OCL形成的支持。 相反，MM患者BMSC中XBP 1的敲低在很大程度上将其病理行为校正到与健康供体BMSC相当的水平。在RO 1基金申请中，我们假设IRE 1 α/XBP 1 s信号传导是调节BMSC炎症特征和BMSC支持MM细胞生长和破骨细胞生成的重要病理生理因素。因此，BMSC中的IRE 1/XBP 1 s信号传导是在治疗MMBD中破坏BMSC对MM细胞生长和骨破坏的支持的潜在治疗靶点。具体目标是： 目标1：确定p38诱导的人XBP 1 s（hXBP 1 s）磷酸化在骨髓基质细胞支持MM细胞生长和破骨细胞生成中的病理生理学意义。 目的2：确定RANKL是否是XBP 1 s的新的转录靶点。 目标3：使用新型免疫活性BMSC特异性Xbp 1 KO小鼠模型，确定BMSC中Xbp 1的缺失是否在体内减弱MM细胞生长和骨吸收。 目标4：确定BMSC中的IRE 1 α内切核糖核酸酶活性是否代表抑制XBP 1生成并破坏BMSC对MM细胞生长和OCL形成的支持的潜在治疗靶点。 这些研究具有多种生物学、病理学和临床意义。首先，我们的研究将为开发和采用靶向IRE 1 α/XBP 1 s信号传导的治疗策略提供重要信息和相关动物模型，例如现有的IRE 1 α抑制剂，和/或炎症激酶诱导的XBP 1 s磷酸化，以破坏MM微环境对MM细胞和OCL的保护作用，作为治疗MMBD的一种手段。其次，这些研究不仅将促进我们对XBP 1 s基础生物学的理解，而且还将提供关于IRE 1 α/XBP 1 s抑制剂对MM患者骨微环境稳态的潜在影响的重要信息。第三，由于基质炎性细胞因子分泌增加是许多炎性骨疾病（如类风湿性骨关节炎和肿瘤骨转移（例如，前列腺癌、乳腺癌和肺癌），我们的研究将提供重要信息和相关动物模型，以研究BMSC中的IRE 1 α/XBP 1 s信号传导是否也是调节基质细胞支持这些炎症性骨病进展的关键病理因素，因此代表了治疗这些炎症性骨病的潜在治疗靶点。

DESCRIPTION (provided by applicant): Multiple myeloma (MM) is the most frequent cancer to involve the skeleton and induces osteolytic lesions that rarely heal in both axial and craniofacial bones. Multiple myeloma bone disease (MMBD) is responsible for some of the most devastating complications of MM and is the major source of morbidity associated with MM. Bone marrow stromal cells (BMSC) are a major type of cells that reside within the MM microenvironment. It has been shown that in MMBD, BMSC produce many growth factors and inflammatory cytokines. These factors can boost the growth of the myeloma tumor cells and activate osteoclasts, the bone resorbing cells, to induce osteolytic lesions in bone. Thus, disrupting the BMSC support of MM cell growth and osteoclast formation is of major clinical significance in treating MMBD. Our long-term goal is to elucidate the molecular mechanisms that regulate BMSC support of MM cell growth and bone destruction in MMBD and identify the potential therapeutic targets for disrupting BMSC support of MMBD. Towards this goal, we have found that a cellular stress molecule spliced X-box-binding protein 1 (XBP1s) is induced in the BMSC derived from MM patients, compared with those from the healthy donors. XBP1s has been shown to control gene expression and/or protein secretion of inflammatory cytokines in other organs and disease models, such as inflammatory bowel disease. We showed recently that elevation of XBP1s protein levels in healthy donor BMSC induced the pathological behavior that are usually present in MM patient BMSCs, such as, heightened inflammatory cytokine secretion, enhanced support of MM cell growth and OCL formation both in vitro and in vivo. Conversely, knockdown of XBP1s in MM patient BMSC largely corrected their pathological behavior to the levels that are comparable to healthy donor BMSC. In this RO1 grant application, we hypothesize that IRE1α/XBP1s signaling is an essential pathophysiological factor that regulates the BMSC inflammatory signature and BMSC support of MM cell growth and osteoclastogenesis. Thus, the IRE1/XBP1s signaling in BMSC is a potential therapeutic target for disrupting BMSC support of MM cell growth and bone destruction in treating MMBD. The Specific Aims are: Aim 1: To determine the pathophysiological significance of p38-induced phosphorylation of human XBP1s (hXBP1s) in BMSC support of MM cell growth and osteoclastogenesis both in vitro and in vivo. Aim 2: To determine whether RANKL is a novel transcriptional target of XBP1s. Aim 3: To determine whether deletion of Xbp1 in BMSC blunts MM cell growth and bone resorption in vivo using a novel immunocompetent BMSC-specific Xbp1 KO mouse model. Aim 4: To determine if the IRE1α endoribonuclease activity in BMSC represents a potential therapeutic target to repress generation of XBP1s and disrupt BMSC support of MM cell growth and OCL formation. These studies have multiple biological, pathological and clinical implications. First, our studies will provide important information and related animal models for developing and employing therapeutic strategies that target the IRE1α/XBP1s signaling, such as the existing IRE1α inhibitors, and/or inflammation kinases-induced phosphorylation of XBP1s to disrupt the protective effects of the MM microenvironment on MM cells and OCL as a means to treat MMBD. Secondly, these studies will not only advance our understanding of basic biology of XBP1s but also provide important information on potential impact of an IRE1α/XBP1s inhibitor on bone microenvironment homeostasis of MM patients. Thirdly, since heightened stromal inflammatory cytokine secretion is a common pathological feature of many inflammatory bone diseases, such as rheumatoid osteoarthritis and tumor bone metastases (e.g., prostate, breast and lung cancers), our studies will provide important information and related animal models to investigate if the IRE1α/XBP1s signaling in BMSC is also a critical pathological factor in regulating the stromal cells support of progress of these inflammatory bone diseases, and thus represents a potential therapeutic targets for treating these inflammatory bone diseases.